The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Cruise control and deceleration fuel cut-off (DFCO) systems are incorporated in vehicles. Cruise control systems enable a vehicle to maintain a desired vehicle speed. DFCO systems disable fuel supply to an engine during certain conditions to cut engine power, improve fuel economy and reduce emissions.
In a cruise control system, a controller maintains the vehicle speed through varying road and vehicle conditions. A vehicle operator may set and manipulate a cruise control target speed through depression of an accelerator pedal, a brake pedal, and/or a clutch pedal, as well as via actuation of hand controls.
When a target speed is set, cruise control systems attempt to maintain a current vehicle speed at approximately the target speed. The current vehicle speed may be different than the target vehicle speed due to various vehicle operating conditions. For example, when traveling on inclined road surfaces, the current vehicle speed may be less than or greater than the target speed.
During a DFCO mode, supply of fuel to an engine is interrupted. The DFCO mode is customarily initiated when engine power is not in demand or engine braking is expected. In other words, the DFCO mode is, typically, initiated when the engine is decelerating. This may occur when an engine control element, such as a throttle valve or an accelerator pedal, is positioned for engine idling. The purpose of this mode of operation is to reduce fuel consumption and maximize engine braking induced by drag or negative torque applied by an engine load. The DFCO mode is generally deactivated when either an engine rotational speed decreases below a predetermined minimum speed associated with idling, or the engine control element is moved from the idling position to accelerate engine rotation and increase engine output torque.
When cruise control is engaged when traveling on a declined surface such as when traveling down a hill, vehicle speed may be higher than a target speed. As a result, a cruise control system may request power reduction. When a vehicle is on a steep enough declined surface, a DFCO mode is triggered. However, the vehicle may be decelerated to a speed that is lower than the target speed. This causes the cruise control system to increase air and fuel supply and thus engine power output. When the engine increases its power by opening throttle position more than a low end threshold, the DFCO mode is deactivated. Toggling of the DFCO mode between ON and OFF states, results in frequent and periodic acceleration and deceleration, which causes unsmooth vehicle speed.